The present invention relates generally to lateral dielectric isolation and more specifically to the process of creating laterally dielectrically isolated islands.
Integrated circuits generally includes epitaxial layers formed on a heavily doped substrate. The epitaxial layer is divided into islands which are laterally dielectrically isolated. This structure is illustrated in FIG. 1. The process of the prior art to form these laterally dielectrically isolated islands includes forming the epitaxial layer on the heavily doped substrate, creating trenches which extend down through the epitaxial layer to the substrate and then filling the trenches by depositing or growing oxide in the trenches. This is followed by an etch back to produce a planar surface. Generally, the tops of the oxides are recessed and therefore it is difficult to form a truly planarized surface.
A typical example of growing lateral dielectric isolation is illustrated in U.S. Pat. No. 4,612,701 to Cox. The filling by oxide deposition is shown in U.S. patent application Ser. No. 07/281,546, filed Dec. 8, 1988, and assigned to the same assignee as the present application. An example of providing lateral dielectric isolation with polycrystalline fill is illustrated in U.S. Pat. No. 4,255,207 to Nicolay et al..
Thus, it is an object of the present invention to provide a method for forming the structure of FIG. 1 without the attendant problems of the prior art.
These and other objects are achieved by forming an insulative layer on the substrate of a first thickness and patterning the insulative layer to form the laterally dielectric walls and exposed island areas of the substrate. The islands are epitaxially grown on the exposed surface of the substrate to a second thickness to form the laterally dielectrically isolated islands. The insulative layer is patterned by using plasma etching. A sacrificial oxide layer is formed over the exposed areas of the substrate and removed with a chemical etch to expose fresh island areas of the substrate for epitaxial deposition.
Impurities of a conductivity type opposite that of the epitaxial layer may be introduced into selective islands to change its conductivity type. Also, exposed areas of the substrate, which is of the same conductivity type as the epitaxial layer, may have opposite conductivity type impurities introduced where the selected islands of the to be changed conductivity type are to be formed to produce a retrograde island.
For islands which include only lateral dielectrical isolation, the first thickness of the dielectric layer and the second thickness of the epitaxial layer are equal to form a planar surface. Where totally dielectrically isolated islands are to be formed, the first epitaxial step forms an epitaxial layer of a second thickness less than the first thickness. This is followed by implanting oxygen into the epitaxial layer to form a horizontal dielectric isolation wall extending laterally between the lateral dielectric walls and displaced from the top surface of the epitaxial island. Subsequent to the oxygen implantation, a second epitaxial step is formed to increase the total thickness of the island to the first thickness of the lateral dielectrical walls.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.